1. Field of the Invention
The present invention concerns a method of making a solid magnetic material from Sm.sub.2 Fe.sub.17 N.sub.3-x type intermetallic nitride powder, where 0.ltoreq.x.ltoreq.1, and where preferably 0.2.ltoreq.x .ltoreq.0.7.
2. Description of the Prior Art
This type of material, recently produced by J. M. D. COEY and sometimes called "Nitromag", has beneficial intrinsic properties:
Curie point: 475.degree. C. PA1 Saturation limit: .mu.o M.sub.s =1.54 T. PA1 Theoretical maximum limit on energy product (BH) (maximum magnetic energy stored): 471 kJ/m.sup.3. PA1 Anisotropic field at room temperature: .mu.o Ha=14 T.
A high coercive field H.sub.c and a high remanent magnetic induction B.sub.r can be achieved with this material.
However, the material is in powder form and the problem arises of converting it to a solid block.
Materials of this type are metastable and break down at temperatures in the order of 600.degree. C. to 650.degree. C., which means that they cannot be shaped by conventional sintering techniques.
The powder material can be bound with a polymer but the resulting composite material has only a low temperature resistance so that it is difficult to use in electric motors. Also, a composite material of this kind ages badly and is relatively hygroscopic, which rules it out for this type of nitride which must be protected from oxidation.
This kind of powder material can also be bound using a metal binder such as zinc, but interaction then occurs between the binder and the magnetic powder material during synthesis of the composite material, with the result that the magnetic properties of the resulting magnet are degraded relative to those of the starting "Nitromag" powder.
An object of the present invention is to propose a method which avoids these drawbacks and produces a solid body which is mechanically stable at temperatures up to 260.degree. C., resistant to oxidation and retains the magnetic properties of the starting powder. A composite material of this kind can therefore be used as magnet, for example in motors.